feat: add cache package for exclude list and health cache YAML read/write

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/cache/cache.go

@@ -0,0 +1,95 @@
+package cache
+
+import (
+	"os"
+	"strings"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+// ExcludeList holds URL prefixes to skip during checking.
+type ExcludeList struct {
+	Domains []string `yaml:"domains"`
+}
+
+// IsExcluded returns true if the URL starts with any excluded prefix.
+func (e *ExcludeList) IsExcluded(url string) bool {
+	for _, d := range e.Domains {
+		if strings.HasPrefix(url, d) {
+			return true
+		}
+	}
+	return false
+}
+
+// LoadExcludeList reads an exclude.yaml file.
+func LoadExcludeList(path string) (*ExcludeList, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	var excl ExcludeList
+	if err := yaml.Unmarshal(data, &excl); err != nil {
+		return nil, err
+	}
+	return &excl, nil
+}
+
+// HealthEntry stores metadata about a single entry.
+type HealthEntry struct {
+	URL        string    `yaml:"url"`
+	Name       string    `yaml:"name"`
+	Status     string    `yaml:"status"` // healthy, inactive, stale, archived, dead
+	Stars      int       `yaml:"stars,omitempty"`
+	Forks      int       `yaml:"forks,omitempty"`
+	LastPush   time.Time `yaml:"last_push,omitempty"`
+	HasLicense bool      `yaml:"has_license,omitempty"`
+	HasReadme  bool      `yaml:"has_readme,omitempty"`
+	CheckedAt  time.Time `yaml:"checked_at"`
+}
+
+// HealthCache is the full YAML cache file.
+type HealthCache struct {
+	Entries []HealthEntry `yaml:"entries"`
+}
+
+// LoadHealthCache reads a health_cache.yaml file. Returns empty cache if file doesn't exist.
+func LoadHealthCache(path string) (*HealthCache, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &HealthCache{}, nil
+		}
+		return nil, err
+	}
+	var hc HealthCache
+	if err := yaml.Unmarshal(data, &hc); err != nil {
+		return nil, err
+	}
+	return &hc, nil
+}
+
+// SaveHealthCache writes the cache to a YAML file.
+func SaveHealthCache(path string, hc *HealthCache) error {
+	data, err := yaml.Marshal(hc)
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(path, data, 0644)
+}
+
+// Merge updates the cache with new entries, replacing existing ones by URL.
+func (hc *HealthCache) Merge(entries []HealthEntry) {
+	index := make(map[string]int)
+	for i, e := range hc.Entries {
+		index[e.URL] = i
+	}
+	for _, e := range entries {
+		if i, exists := index[e.URL]; exists {
+			hc.Entries[i] = e
+		} else {
+			hc.Entries = append(hc.Entries, e)
+		}
+	}
+}